Liquid crystal displays (LCDs) generally display images by transmitting or blocking light through the action of liquid crystals. LCDs have been used in a variety of computing displays and devices, including notebook computers, desktop computers, tablet computing devices, mobile phones (including smart phones) automobile in-cabin displays, on appliances, as televisions, and so on. LCDs often use an active matrix to drive liquid crystals in a pixel region. In some LCDs, a thin-film transistor (TFT) is used as a switching element in the active matrix.
FIG. 1 illustrates a perspective view of a sample electronic device, such as a tablet computer. The electronic device includes a touch screen display 100 enclosed by a housing 138. The touch screen display 100 incorporates a touch panel 102 and an LCD, although alternative embodiments may employ an OLED layer instead of an LCD. The LCD is not shown in FIG. 1. Although a tablet computing device is illustrated in FIG. 1, it should be appreciated that the discussion herein may be equally applicable to any display and/or electronic device incorporating a display, such as a smart phone, notebook or laptop computer, all-in-one computing device, personal digital assistant, multimedia player, e-book reader, and so on.
FIG. 2 illustrates a cross-sectional view of a sample tablet computing device shown in FIG. 1 (the cross-section is shown by arrows 2-2 in FIG. 1). LCD 204 includes an array of pixels and an array of TFTs associated with the pixels. The LCD 204 may be coupled to the touch panel 102 by an optically clear adhesive (OCA) 206 or may have an air gap from the touch panel.
The LCD 204 may suffer from display noise, which may cross-couple to a capacitive touch sensing subsystem of the tablet computing device or other electronic device. Essentially, the capacitance between the gate and drain of a TFT for a given pixel may vary with a gate floating voltage, which depends upon the touch sensing subsystem, and thus acts as a parasitic capacitance on that subsystem. Thus, the display noise may interfere with detection of touches or other capacitive sense events during operation. For example, the display noise in the LCD 204 may be sensitive to finger touching on the touch panel 102. For example, a finger may be relatively cold or warm. The device 100 may be used in a hot and humid environment, or a cold and dry environment. It is desirable to develop techniques to reduce the display noise.